1. Field
The present invention relates to a washing machine including a balancer, and more particularly, to a washing machine capable of reducing a vibration of a water tub due to an eccentric state, that is, an unbalance, which may occur at the time of rotation of a rotation tub, and a method of controlling the same.
2. Description of the Related Art
In general, a washing machine (generally, a drum-shaped washing machine) includes a water tub which contains water (washing water or rinsing water) therein, a rotation tub which is rotatably installed in the water tub and contains laundry therein, and a motor which generates a driving force to rotate the rotation tub. The washing machine washes the laundry by an operation of rising and dropping the laundry contained therein along an inner wall of the rotation tub when the cylindrical rotation tub is rotated.
Such a washing machine washes the laundry using a series of operations including a washing mode to wash dirt out of the laundry using water in which a detergent is dissolved (i.e., washing water), a rinsing mode to rinse bubble or residual detergent out of the laundry using water in which the detergent is not dissolved (i.e., rinsing water), and a dehydrating mode to dehydrate the laundry at a high speed. In the dehydrating mode, if the rotation tub is rotated at a high speed in a state in which the laundry is unevenly distributed along an inner wall of the rotation tub and thus an unbalance or imbalance occurs, a force is biased toward a rotation shaft of the rotation tub to generate a large vibration.
In order to prevent the vibration due to such an unbalance, a washing machine including a race which is provided to be concentric with a rotation tub and a balancer having a plurality of balls seated in the race together with oil is disclosed in Japanese Unexamined Patent Application Publication No. 10-43472.
In the washing machine disclosed in the above Publication, when the rotation tub is rotated at a high speed, the balls are automatically moved in the race to prevent the force from being biased toward the rotation shaft such that the unbalance is removed.
However, in the washing machine including the balancer as described above, if the weight of the unbalance is larger than the total weight of the balls, the unbalance cannot be sufficiently removed even if the balls are located opposite the unbalance in the circumferential direction (opposite phase). Thus, the vibration occurs.
If the number of rotations of the rotation tub is less than an inherent number of vibrations of the rotation tub, a difference occurs between a movement speed of the balls and a movement speed of the unbalance (i.e., the rotation speed of the rotation tub), and thus a relative position between the unbalance and the balls periodically varies.
At this time, if the balls and the unbalance are arranged in phase with each other in the circumferential direction (in-phase), a larger force is applied to the rotation shaft to generate a larger vibration. If the balls and the unbalance are arranged in phase with each other at a time point when the number of rotations of the rotation tub coincides with the inherent number of vibrations, resonance becomes large enough to generate an excessive vibration of the water tub.